This application relates to diagnostic radiation systems such as x-ray systems. More specifically, this application relates to methods and apparatus for monitoring the operation of diagnostic radiation systems.
Ever since Wilhelm Rontgen discovered x rays and successfully imaged his wife's hand to show the structure of her bones, radiation has been used as a medical diagnostic tool. While two-dimensional radiographs were used for decades, such images suffered from the superposition of images of structures outside the specific region of interest and were generally produced images that were limited to particular image planes.
More recent advances have resulted in the development of tomographic techniques, particularly as embodied in computed-tomography (“CT”) imaging devices and in computed axial tomography (“CAT”) imaging devices. Since their introduction in the 1970's, tomographic imaging devices have become widely used for both diagnostic and preventive medical applications. In addition to perform CT and CAT scans to confirm suspected diagnoses of tumors, infarction, bone trauma, and the like, scanning using such devices is now almost routine for patients at high risk for certain medical conditions such as colon cancer and heart disease. Indeed, some institutions offer full-body scans to the general public as part of a generalized effort for early detection of disease.
While such efforts have had a significant impact in allowing physicians to detect disease early and to confirm diagnoses without invasive techniques, they are not without a number of concerns. One particular concern results from the fact that x rays are a form of ionizing radiation that have their own impact on the body being measured. Since the early 1980's, the per capita dose of radiation from medical imaging has increased by a factor of almost six. Some estimates suggest that the current level of usage of CT scans will result in an increase in cancer mortality rate of 1.5% to 2% from cancers caused by the scans. While the benefit of reducing cancer mortality from early detection of cancers significantly exceeds this rate, it remains a concern.
Monitoring the actual dose delivered to patient is complicated by a number of factors. The dose depends on multiple known factors that include the volume and type of tissue scanned, the build of the patient scanned, the number and type of scan sequences, and the quality of images to be produced. There is, moreover, a lack of uniformity among machines used to perform the scans, varying not only among manufacturers but also being sufficiently complex devices to have individual variations in uniformity. The dose received by a patient depends on how the machines are used and how different settings for a particular imaging session are configured.
In addition to these patient concerns, there are concerns about the machines themselves. The x-ray tube, for example, tends to degrade over time as the machine is used. To obtain a similar image quality, a machine tends to need to be operated at higher current (mA) as the efficiency of the tube decreases. It is desirable to be able to predict when tube operational quality is likely to become so low that replacement is needed.
There are, thus, a number of deficiencies in the art that it is desirable to address.